Field of the Invention
The present invention generally relates to devices used in the treatment of hydrocephalus, and more particularly, to improvements to shunts and siphon control devises used to help divert and regulate excess fluid during the treatment therapy.
Description of the Related Art
The human brain includes four ventricles. Each ventricle contains a choroid plexus that produces cerebrospinal fluid (CSF) which bathes and cushions the brain and spinal cord within their bony and non-elastic confines.
In a normal healthy person, CSF continuously circulates through and around the brain and its ventricles and around the spinal cord and is continuously drained away into the circulatory system so that a controlled pressure is continually maintained within the system. The CSF flows from the lateral ventricles via the foramina of Monro into the third ventricle, and then the fourth ventricle via the cerebral aqueduct in the brainstem. From there it normally can pass into the central canal of the spinal cord or into the cisterns of the subarachnoid space via three small foramina: the central foramen of Magendie and the two lateral foramina of Luschka.
The aqueduct between the third and fourth ventricles is very small, as are the foramina and both are therefore susceptible to becoming blocked or restricted, commonly due to a birth defect, or a local growth, such as that caused by a tumor or infection, thereby disrupting the normal CSF flow. When the CSF flow is impeded, the continued production of CSF will cause an increase in intracranial pressure as the fluid collects within the ventricles.
Alternatively, a similar increase in intracranial pressure of the patient may result from an overproduction of the CSF fluid, from a congenital malformation, or from complications of head injuries or infections, or in some cases, by malabsorption. In any case, the result is the same, an increase of CSF fluid within the ventricles and an increase in intracranial pressure. This condition is called hydrocephalus.
When the CSF accumulates in the cerebral ventricles, the increased volume of fluid compresses the patient's brain tissue since the patient's skull will not yield to this unplanned expansion of fluid. Unfortunately, this compression destroys more and more brain tissue and a variety of secondary symptoms will become apparent in the patient as the neurological functions effectively shut down. These include, headaches, vomiting, dizziness, slurred speech, photophobia/light sensitivity, and in more severe cases, seizures, loss of consciousness and even death.
Hydrocephalus is often treated by the insertion of a diverting catheter into the ventricles of the brain or into the lumbar cistern. Such a catheter or shunt is connected by a regulating valve to a distal catheter which shunts the CSF to another space where it can be reabsorbed and the excess pressure within the brain released. Examples of common diversion sites include the peritoneum of the abdomen via a ventriculoperitoneal shunt or lumboperitoneal shunt or the atrium of the heart via a ventriculoatrial shunt.
A commonly used shunt to treat hydrocephalus is called the Spitz-Holter shunt. It is a conduit that is positioned between the patient's brain and the patient's heart. The device includes a tiny one-way valve that allows a controlled amount of CSF to leave the lateral ventricle of the brain and enter the heart and thereby prevent the increased pressure that causes such damage to the tissues of the brain. This device has helped millions survive this potentially fatal condition since the late 1950s.
About 50% of the shunts fail within the first 5 years after implantation independent of the shunt operating principle and the hydrocephalus etiology. Such shunt failure requires a revision of the shunt system within the patient to avoid a return of original hydrocephalus symptoms. The main causes of failure are infection of the shunt system, obstruction of the shunt, and over-drainage and under-drainage of CSF within the shunt system.
Over-drainage results in an excessive average flow of CFS through the shunt system. This condition may generate an abnormally low intra-cranial pressure, a collapse of the parenchyma and sub-arachnoid hemorrhage.
Some shunt systems use a “Codman® Hakim® valve” or a “Codman® Certas™” programmable valve, which are commercially available from Codman & Shurtleff, Inc. of Raynham, Mass. The Codman® Hakim® and the Codman® Certas™ valve allows a doctor to adjust the valve opening pressure non-invasively after implantation.
Effective fluid flow rate control is particularly important since over-drainage of cerebrospinal fluid can result in dangerous conditions, including subdural hematoma. Over-drainage tends to occur when a patient moves from a horizontal position to a sitting or standing position, due to a siphon effect in the shunt system. To reduce the risk of over-drainage, some shunt systems include additional devices, sometimes referred to as anti-siphon devices, for preventing over-drainage. Some such devices use weights, which move in response to the patient changing position, to open or close the fluid flow path. One system, described in U.S. Pat. No. 5,368,556 (Lecuyer), includes spherical weights which provide additional compressive force against a valve spring to help maintain the valve in a closed position when the patient is sitting or standing. However, noise associated with the use of such weights may be objectionable. Other systems, such as the SIPHONGUARD® Anti-Siphon and Flow-Control Device, as described in U.S. Pat. No. 6,126,628, provides a dual pathway, ball and spring anti-siphon device. The primary pathway is controlled by a ball 110 that is biased by a flat spring bias element 114 and a coil spring counterbias element 112.
For a shunt system with a differential pressure (DP) valve set to 100 mmH2O and connected to a simple gravity actuated valve that requires 200 mmH2O to open in the vertical position. The valve is calibrated to add either 0 mmH2O when horizontal or 200 mmH2O when in the vertical position. Fluid will be driven through the system and into the peritoneal (distal) catheter to drain when the differential pressure exceeds the threshold 100 mmH2O (DP valve setting) in the horizontal position or 300 mmH2O (100 mmH2O valve+200 mmH2O anti-siphon device) when in the vertical position. The anti-siphon device will therefore prevent any fluid drainage until the 300 mmH2O threshold is exceeded.
A drainage problem manifests itself when a patient is not completely vertical (i.e. sleeping on a pillow or bedridden), due to gravity the weighted balls will close off the single fluid pathway and prevent fluid drainage, causing a potentially high increase in the patients ICP such that severe headaches develop, or worse. This will continue until the threshold pressure of 300 mmH2O is exceeded or the anti-siphon device becomes oriented in the horizontal position to open the single fluid pathway.
With the proposed Bi-Phase Fluid Surge Suppressor device, the above drainage problem is mitigated. With a Bi-Phase valve set to 200 mmH2O (in the vertical position), and one has a differential pressure (DP) valve set to 100 mmH2O. When the patient is positioned such that the weighted balls of the Bi-Phase device close the primary pathway, the always open higher resistive secondary pathway allows CSF fluid to drain (when the threshold DP of 100 mmH2O only is exceeded).
Should a patient stand upright (vertical position), the entire system would control the hydrostatic siphoning effect until the threshold of 300 mmH2O (100 mmH2O DP valve+200 mmH2O Bi-Phase device) is exceeded. Once exceeded, the Bi-Phase device continues to suppress the surge of fluid until the pressure decreases and the weighted balls seat themselves to close off the primary pathway, while still allowing slow gradual drainage through the secondary pathway until the differential pressure falls below the 100 mmH2O DP valve setting, in this example.